Electric power steering controller

Abstract

An electric motor controller for a steering device that can apply an appropriate steering force to a steering wheel according to running conditions. An electric power steering controller of the present invention includes a steering shaft reaction force torque sensor for detecting a reaction force torque of a steering system, a superimposed reaction force torque calculating unit for multiplying a steering angle detected by the steering angle sensor by a gain to calculate a superimposed reaction force torque in the return direction of the steering wheel, and a control unit for controlling the gain so that the superimposed reaction force torque is reduced when a reaction force torque of the steering system is increased and the superimposed reaction force torque is increased when a reaction force torque of the steering system is decreased.

1. An electric power steering controller comprising:
 a road surface reaction force torque detecting unit for detecting reaction force torque of a road surface on which a vehicle having a steering system including said electric power steering controller travels;  
 a reaction force torque detecting unit for detecting reaction force torque of the steering system, said reaction force torque detecting unit including a steering shaft reaction force torque sensor for detecting the reaction force torque of a steering shaft of the steering system; and  
 a return torque compensator for calculating a compensating return torque superimposed on the reaction force torque in returning a steering wheel of the steering system in a return direction toward a neutral position of the steering wheel, said return torque compensator calculating the compensating return torque by multiplying the reaction force torque of the road surface detected by said road surface reaction torque detecting unit by a feedback gain varying with the reaction force torque so that the compensating return torque superimposed on the reaction force torque changes inversely with magnitude of the reaction force torque of the steering shaft.  
 
   
   
     2. The electric power steering controller according to  claim 1 , wherein said feedback gain becomes smaller when the magnitude of the reaction force torque of the steering shaft exceeds a threshold value.